Under certain conditions, simultaneous drilling and reaming in a well bore is often desirable. Depending on formation characteristics, simultaneous drilling and reaming may offer faster penetration rates than drilling alone, or may reduce total rig time for drilling and reaming when reaming is needed. For certain formations, reaming may be needed for achieving a well bore that achieves a desired degree of smoothness or circularity. Smoothness and circularity may be important for packers to seal off selected formation layers.
Simultaneous drilling and reaming is also used for drilling a wide borehole below a narrow constriction such as a casing shoe. A bottom hole assembly including a drill bit and a reamer is selected to have a diameter less than the diameter of an aperture of the constriction, so that the bottom hole reaming can be done without drilling out the constriction. The drill bit passes through the aperture to drill a pilot hole for the reamer. Once the reamer passes through the aperture, cutters of the reamer are expanded to a diameter larger than the diameter of the aperture, so that the reamer enlarges the pilot hole to a diameter greater the diameter of the aperture.